1. Field of the Invention
This invention relates to a security document with a security element having at least a first layer with gaps in the form of characters or patterns, and a magnetic layer disposed below said first layer. The invention relates further to such a security element and to methods for producing said element and the document.
2. Discussion of Related Technology
It has been known for some time to provide security documents with plastic security threads having a magnetic coating and thus serving as a machine-readable security feature (DE 16 96 245 A1, EP 0 310 707 A1).
To increase the forgery-proofness of this proven security feature further, it has also been proposed to provide the magnetic coating on the carrier material in discontinuous form. For example EP 0 407 550 A1 describes a security document with an embedded security thread provided with a binary code consisting of magnetic material. Certain bit lengths are defined which are constant over the total length of the strip. The coating of a bit length with magnetic material corresponds for example to a 1 while a bit length without magnetic material corresponds to a 0. The binary code known from EP 0 407 550 A1 is characterized in that it is composed of alternatingly disposed separation segments and word segments whereby the word portion consists of a certain number of bit lengths and the sequence of binary values of the separation segments must not occur within this word length in order to permit clear detection of the word segments.
This security element has the disadvantage, however, that there is no possibility of fast visual checking as is necessary in many situations of daily life.
It has therefore likewise been proposed to combine machine-testable security features with visual features. EP 0 516 790 A1 discloses a security document with such a security element. The security thread described here consists of a transparent plastic carrier layer with a metallic coating in which gaps are provided in the form of characters or patterns, the so-called negative writing. If the thread is present in the paper pulp, these gaps and the metallic surroundings are hardly visible when viewed by reflected light. When viewed by transmitted light, however, the transparent gaps stand out in strong contrast from their opaque surroundings and are thus easily recognized. At the same time the security element has a magnetic coating which can e.g be disposed congruently below the metal layer so that the gaps are present congruently in both layers. In this case a transparent plastic foil is first printed in the area of the later gaps with an activable ink containing foamable additives for example. Subsequently the plastic foil is provided in consecutive working steps first with a first metal layer, a magnetic layer and a second metal layer. Subsequent activation of the ink, e.g. thermal action, causes the layers to be removed in the area of the activable ink so that the gaps arise.
Alternatively the magnetic coating can be provided below the metal layer only in the edge areas of the thread and along the running direction of the element in the document, the gaps being disposed in the metal layer in the intermediate areas free from the magnetic layer. The transparent carrier foil of the thread is printed in the edge areas with magnetic material in the form of strips. In the intermediate areas free from the magnetic layer the activable ink is applied in the form of the later gaps and the carrier foil then coated all over with the metal layer. The following activation of the ink finally gives rise to the gaps in the metal layer.
The invention is based on the problem of proposing a security document with a security element which allows not only a visual check but also machine testing and offers increased protection from forgery.